Ballista catapult

Roll Tube Ballista

A ballista is a type of Roman battlefield weapon which fires very big arrows or spears. There are lots of different types of these weapons which are based on a ‘catapult’ type idea which uses a stretched or twisted material to store energy like a spring then suddenly release it to propel an object eg. a boulder.

Here are some roll tube and plastic strip catapults which can fire ping pong balls or rolled up paper ‘boulders’.

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ballista a
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You will need 6 paper roll tubes (A5 short) and 3 wooden dowels 6mm diameter x 150mm long.

The holes must be accurately punched in the ends of the roll tubes so that they are in line!

The tubes and dowels fold together to make a triangular prism which is a very strong structure and resembles the ‘tree trunk’ structure of a real siege weapon of the period.

The ‘throwing arm’ needs to be stronger than a simple roll tube so an A5 long piece of card can be used or 3 sheets of A5 long paper rolled together!

A piece of card A7 size can be used to create a cup or box shape to hold the boulder which is to be fired from the catapult.

A single elastic band is all that is required to fire the catapult!

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This is a much sturdier version of the catapult made from plastic (corriflute) strips and wooden dowels.

The throwing arm is made from a strip of 12mm squre section softwood about 20cm long.

How far will it fire?

How can you increase the range of your catapult?

How can you alter the firing angle so the boulder will drop over the top of some castle walls instead of hitting the walls?

What other siege machines could you design to bombard and sieze a castle from your enemies?


Leonardo Da Vinci made all sorts of drawings of siege weapons and even submarines for warfare around about 1500AD.

The ancient Greeks, Egyptians and Romans all made amazing mechanical inventions for defence and attack.

It is said that ‘Archimedes’ designed a giant claw which could be lowered down to destroy ships attacking his coastal fortress.

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